L is for Light
To investigate how light is reflected from mirrored surfaces.
NATIONAL SCIENCE EDUCATION STANDARD:
Physical Science, Grades 5–8, Transfer of Energy: “Light interacts with matter by trans- mission (including refraction), absorption, or scattering (including reflection).”
small flashlights (penlights work well)
pocket mirrors (approximately 2 3 inches)
large cardboard boxes or blocks or textbooks
Check to see that the edges of the pocket mirrors are not sharp. Cover the edges with masking tape as needed to prevent cuts.
Review with students what they learned about how light travels in “L is for Light.” (It travels as waves.) Tell them that today they will learn more about how light travels and what happens to it when it strikes a mirrored surface.
Distribute a pocket mirror and a flashlight to each student or pair of students. Have them try shining lights on the mirrors in as many ways as they can and record what they learn about how light reflects off mirrors.
Hold a discussion about what students learned in their investigations. As a class, come up with a list of rules that describe how light behaves. (Light bounces off a mirror at the same angle it strikes the mirror.) Introduce the Law of Reflection, and the terms angle of incidence and angle of reflection.
Now challenge students to use what they learned about how light waves travel to design a maze for light to travel through. (They can use wooden blocks or heavy books to prop up the mirrors, or cut cardboard pieces to fit like walls inside a cardboard box.) By placing mirrors in the corners on the maze, students can direct the light through a complicated course.
Have students draw maps of their mazes, showing the locations of the mirrors and the approximate angles of incidence and reflection. Ask students to explain their mazes and the paths of reflected light.
Judge the mirror mazes according to the grade level of your class. Older students may be able to construct mazes with more mirrors than younger students.
Have students research what it is about mirrors than allows them to reflect the images of objects placed in front of them. (Light shined on a surface will always be reflected back at the same angle at which it hits the surface. [See the top illustration at the left.] This is called the law of reflection. You see yourself in a mirror because all the light rays are reflected at the same angle. Reflection from a smooth surface is called specular reflection. Reflection of light from a rough surface, on the other hand, is called diffuse reflection. When light shines on a rough or dull surface, the light rays still get reflected back at the same angle at which they struck the surface, but since the surface is made up of
many small uneven surfaces, the light bounces off of it at many differ- ent angles. [See the bottom illustration at the left.] Since the light is reflected at many different angles, it cannot form an image. This is why rough and dull surfaces cannot be used as mirrors.)